In many gas utilization systems the precise control of gas flow is essential. This is particularly true in the field of plasma etching of silicon wafers. Plasma etching also known as dry processing uses various types of gases such as carbon tetrachloride and chlorine to etch or remove unwanted materials from a silicon wafer which is being processed into integrated circuits. The type of gas used depends on the types of materials to be removed from the wafer as well as the type of etching desired, e.g., anistropic or isotropic. Often two or more etching gases are required to complete a single etching operation. The gases may be used in sequence or combined. The time of etching is critical to control the amount of material removed. Equally important is control of the flow of gases into the etching chamber so that precise control of volume of a gas in the etching chamber may be known. This enables an operator to maintain exact control of the amount of each gas used and where two or more gases are used control of the relative percentages thereof.
Typical gas flow controllers such as flowmeters are often inadequate to provide the precise gas flow control required in dry processing.
The present invention provides a gas flow controller of general utility but having particular utility in the field of dry processing of silicon wafers.